Compound interest calculator
Separate your own deposits from calculated interest, and compare beginning- and end-of-month contributions.
$1,000.00 starting balance · $200.00 each month · 120 months · 4% nominal annual interest · deposits at month end
Check your rate assumption
Same deposits, timing and horizon. These are hypothetical rates, not forecasts or a likely range.
View all 120 monthly rows
| Month | Opening | Deposit | Interest | Closing |
|---|---|---|---|---|
| 1 | $1,000.00 | $200.00 | $3.33 | $1,203.33 |
| 2 | $1,203.33 | $200.00 | $4.01 | $1,407.34 |
| 3 | $1,407.34 | $200.00 | $4.69 | $1,612.04 |
| 4 | $1,612.04 | $200.00 | $5.37 | $1,817.41 |
| 5 | $1,817.41 | $200.00 | $6.06 | $2,023.47 |
| 6 | $2,023.47 | $200.00 | $6.74 | $2,230.21 |
| 7 | $2,230.21 | $200.00 | $7.43 | $2,437.65 |
| 8 | $2,437.65 | $200.00 | $8.13 | $2,645.77 |
| 9 | $2,645.77 | $200.00 | $8.82 | $2,854.59 |
| 10 | $2,854.59 | $200.00 | $9.52 | $3,064.11 |
| 11 | $3,064.11 | $200.00 | $10.21 | $3,274.32 |
| 12 | $3,274.32 | $200.00 | $10.91 | $3,485.23 |
| 13 | $3,485.23 | $200.00 | $11.62 | $3,696.85 |
| 14 | $3,696.85 | $200.00 | $12.32 | $3,909.17 |
| 15 | $3,909.17 | $200.00 | $13.03 | $4,122.20 |
| 16 | $4,122.20 | $200.00 | $13.74 | $4,335.95 |
| 17 | $4,335.95 | $200.00 | $14.45 | $4,550.40 |
| 18 | $4,550.40 | $200.00 | $15.17 | $4,765.57 |
| 19 | $4,765.57 | $200.00 | $15.89 | $4,981.45 |
| 20 | $4,981.45 | $200.00 | $16.60 | $5,198.06 |
| 21 | $5,198.06 | $200.00 | $17.33 | $5,415.38 |
| 22 | $5,415.38 | $200.00 | $18.05 | $5,633.44 |
| 23 | $5,633.44 | $200.00 | $18.78 | $5,852.21 |
| 24 | $5,852.21 | $200.00 | $19.51 | $6,071.72 |
| 25 | $6,071.72 | $200.00 | $20.24 | $6,291.96 |
| 26 | $6,291.96 | $200.00 | $20.97 | $6,512.93 |
| 27 | $6,512.93 | $200.00 | $21.71 | $6,734.64 |
| 28 | $6,734.64 | $200.00 | $22.45 | $6,957.09 |
| 29 | $6,957.09 | $200.00 | $23.19 | $7,180.28 |
| 30 | $7,180.28 | $200.00 | $23.93 | $7,404.22 |
| 31 | $7,404.22 | $200.00 | $24.68 | $7,628.90 |
| 32 | $7,628.90 | $200.00 | $25.43 | $7,854.33 |
| 33 | $7,854.33 | $200.00 | $26.18 | $8,080.51 |
| 34 | $8,080.51 | $200.00 | $26.94 | $8,307.44 |
| 35 | $8,307.44 | $200.00 | $27.69 | $8,535.13 |
| 36 | $8,535.13 | $200.00 | $28.45 | $8,763.58 |
| 37 | $8,763.58 | $200.00 | $29.21 | $8,992.80 |
| 38 | $8,992.80 | $200.00 | $29.98 | $9,222.77 |
| 39 | $9,222.77 | $200.00 | $30.74 | $9,453.51 |
| 40 | $9,453.51 | $200.00 | $31.51 | $9,685.03 |
| 41 | $9,685.03 | $200.00 | $32.28 | $9,917.31 |
| 42 | $9,917.31 | $200.00 | $33.06 | $10,150.37 |
| 43 | $10,150.37 | $200.00 | $33.83 | $10,384.20 |
| 44 | $10,384.20 | $200.00 | $34.61 | $10,618.82 |
| 45 | $10,618.82 | $200.00 | $35.40 | $10,854.21 |
| 46 | $10,854.21 | $200.00 | $36.18 | $11,090.39 |
| 47 | $11,090.39 | $200.00 | $36.97 | $11,327.36 |
| 48 | $11,327.36 | $200.00 | $37.76 | $11,565.12 |
| 49 | $11,565.12 | $200.00 | $38.55 | $11,803.67 |
| 50 | $11,803.67 | $200.00 | $39.35 | $12,043.01 |
| 51 | $12,043.01 | $200.00 | $40.14 | $12,283.16 |
| 52 | $12,283.16 | $200.00 | $40.94 | $12,524.10 |
| 53 | $12,524.10 | $200.00 | $41.75 | $12,765.85 |
| 54 | $12,765.85 | $200.00 | $42.55 | $13,008.40 |
| 55 | $13,008.40 | $200.00 | $43.36 | $13,251.76 |
| 56 | $13,251.76 | $200.00 | $44.17 | $13,495.94 |
| 57 | $13,495.94 | $200.00 | $44.99 | $13,740.92 |
| 58 | $13,740.92 | $200.00 | $45.80 | $13,986.73 |
| 59 | $13,986.73 | $200.00 | $46.62 | $14,233.35 |
| 60 | $14,233.35 | $200.00 | $47.44 | $14,480.79 |
| 61 | $14,480.79 | $200.00 | $48.27 | $14,729.06 |
| 62 | $14,729.06 | $200.00 | $49.10 | $14,978.16 |
| 63 | $14,978.16 | $200.00 | $49.93 | $15,228.09 |
| 64 | $15,228.09 | $200.00 | $50.76 | $15,478.85 |
| 65 | $15,478.85 | $200.00 | $51.60 | $15,730.44 |
| 66 | $15,730.44 | $200.00 | $52.43 | $15,982.88 |
| 67 | $15,982.88 | $200.00 | $53.28 | $16,236.15 |
| 68 | $16,236.15 | $200.00 | $54.12 | $16,490.27 |
| 69 | $16,490.27 | $200.00 | $54.97 | $16,745.24 |
| 70 | $16,745.24 | $200.00 | $55.82 | $17,001.06 |
| 71 | $17,001.06 | $200.00 | $56.67 | $17,257.73 |
| 72 | $17,257.73 | $200.00 | $57.53 | $17,515.25 |
| 73 | $17,515.25 | $200.00 | $58.38 | $17,773.64 |
| 74 | $17,773.64 | $200.00 | $59.25 | $18,032.88 |
| 75 | $18,032.88 | $200.00 | $60.11 | $18,292.99 |
| 76 | $18,292.99 | $200.00 | $60.98 | $18,553.97 |
| 77 | $18,553.97 | $200.00 | $61.85 | $18,815.82 |
| 78 | $18,815.82 | $200.00 | $62.72 | $19,078.54 |
| 79 | $19,078.54 | $200.00 | $63.60 | $19,342.13 |
| 80 | $19,342.13 | $200.00 | $64.47 | $19,606.61 |
| 81 | $19,606.61 | $200.00 | $65.36 | $19,871.96 |
| 82 | $19,871.96 | $200.00 | $66.24 | $20,138.20 |
| 83 | $20,138.20 | $200.00 | $67.13 | $20,405.33 |
| 84 | $20,405.33 | $200.00 | $68.02 | $20,673.35 |
| 85 | $20,673.35 | $200.00 | $68.91 | $20,942.26 |
| 86 | $20,942.26 | $200.00 | $69.81 | $21,212.06 |
| 87 | $21,212.06 | $200.00 | $70.71 | $21,482.77 |
| 88 | $21,482.77 | $200.00 | $71.61 | $21,754.38 |
| 89 | $21,754.38 | $200.00 | $72.51 | $22,026.90 |
| 90 | $22,026.90 | $200.00 | $73.42 | $22,300.32 |
| 91 | $22,300.32 | $200.00 | $74.33 | $22,574.65 |
| 92 | $22,574.65 | $200.00 | $75.25 | $22,849.90 |
| 93 | $22,849.90 | $200.00 | $76.17 | $23,126.07 |
| 94 | $23,126.07 | $200.00 | $77.09 | $23,403.15 |
| 95 | $23,403.15 | $200.00 | $78.01 | $23,681.17 |
| 96 | $23,681.17 | $200.00 | $78.94 | $23,960.10 |
| 97 | $23,960.10 | $200.00 | $79.87 | $24,239.97 |
| 98 | $24,239.97 | $200.00 | $80.80 | $24,520.77 |
| 99 | $24,520.77 | $200.00 | $81.74 | $24,802.51 |
| 100 | $24,802.51 | $200.00 | $82.68 | $25,085.18 |
| 101 | $25,085.18 | $200.00 | $83.62 | $25,368.80 |
| 102 | $25,368.80 | $200.00 | $84.56 | $25,653.36 |
| 103 | $25,653.36 | $200.00 | $85.51 | $25,938.87 |
| 104 | $25,938.87 | $200.00 | $86.46 | $26,225.33 |
| 105 | $26,225.33 | $200.00 | $87.42 | $26,512.75 |
| 106 | $26,512.75 | $200.00 | $88.38 | $26,801.13 |
| 107 | $26,801.13 | $200.00 | $89.34 | $27,090.46 |
| 108 | $27,090.46 | $200.00 | $90.30 | $27,380.77 |
| 109 | $27,380.77 | $200.00 | $91.27 | $27,672.04 |
| 110 | $27,672.04 | $200.00 | $92.24 | $27,964.28 |
| 111 | $27,964.28 | $200.00 | $93.21 | $28,257.49 |
| 112 | $28,257.49 | $200.00 | $94.19 | $28,551.68 |
| 113 | $28,551.68 | $200.00 | $95.17 | $28,846.85 |
| 114 | $28,846.85 | $200.00 | $96.16 | $29,143.01 |
| 115 | $29,143.01 | $200.00 | $97.14 | $29,440.15 |
| 116 | $29,440.15 | $200.00 | $98.13 | $29,738.29 |
| 117 | $29,738.29 | $200.00 | $99.13 | $30,037.41 |
| 118 | $30,037.41 | $200.00 | $100.12 | $30,337.54 |
| 119 | $30,337.54 | $200.00 | $101.13 | $30,638.66 |
| 120 | $30,638.66 | $200.00 | $102.13 | $30,940.79 |
Illustrative calculations, not financial advice or a lender quote. See the assumptions and limitations below.
What this calculation assumes
Constant nominal annual interest, compounded monthly. The rate is an input for a hypothetical scenario; it is not an investment forecast. No withdrawals are modeled.
The formula
End-of-month balance = P(1 + r)ⁿ + D × [(1 + r)ⁿ − 1] ÷ r. Beginning-of-month deposits multiply only the deposit term by (1 + r).
P is starting savings, D is the recurring monthly deposit, n is months and r is annual percentage ÷ 1,200. At 0%, balance = P + nD.
Timing and rounding
For end-of-month deposits, interest is applied to the opening balance before adding the deposit. For beginning-of-month deposits, the deposit earns that month’s interest too. Full precision is retained until display.
Where the model stops
This model does not capture market volatility, investment losses, changing rates, tax, fees or inflation. A nominal annual rate is not APY. It assumes every deposit happens on time.
Questions about this tool
Can I enter APY as the annual rate?
This input expects a nominal annual rate. If you know APY, the equivalent monthly rate is (1 + APY/100)^(1/12) − 1; multiply it by 1,200 to express a nominal annual percentage.
Why show contributions separately?
A large ending balance can come mostly from money you added. The breakdown shows how much of the projection is contributions and how much is calculated interest.
Check the method
See our calculation and testing notes, or report a reproducible discrepancy.
Conceptual reference: Investor.gov: Compound interest calculator. This source is not an endorsement of SimpleFinCalc or a validation of its outputs.